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  • 1
    Electronic Resource
    Electronic Resource
    Evidences for extended sources and temporal modulations in molecular observations of C/1995 O1 (Hale-Bopp) at the IRAM interferometer (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 63-63 
    Details
    ISSN: 1573-0794
    Keywords: Radio interferometry ; spatial distribution ; extended sources ; nucleus rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Comet C/1995 O1 (Hale-Bopp) has been observed on October 5 and 25, 1996 and from March 6 to March 22, 1997 with the Institut de Radioastronomie Millimétrique (IRAM) interferometer at Plateau de Bure (France). Millimetre lines of HCN,HNC, CO, H2CO, CH3OH, H2S, CS and SO were mapped with spatial resolutions of 1.5–3.5 arc sec. These observations allow us to investigate whether these species are released by the nucleus or produced in the coma by extended sources or photo-processes. The brightness distribution of the HCN J (1-0) line is consistent with release from the nucleus. The HNC J (1-0) distribution deviates from that of HCN in the innermost coma, and indicates production of HNC in the coma. This is in agreement with the heliocentric variation of the HNC/HCN ratio (Biver et al., 1997, Science 275, 1915; Irvine et al., 1998, this issue) and formation by chemical reactions (Rodgers and Charnley, 1998, Ap. J. 501, L227; Irvine et al., 1998, Nature 393, 547). There is clear evidence that SO is a photo dissociation product. The observations also confirm that H2CO is mainly produced by an extended source, as first evidenced in comet P/Halley. The contribution of the nucleus to the total H2CO production rate does not exceed 6%. The molecular lines have also been monitored hourly with the five antennas of the interferometer in single-dish mode. The line velocity shifts show aperiodic modulation linked to the nucleus rotation. The amplitude of the modulation differs from one species to another. The periodic modulation seen for the CO J (2-1) line on March 11 suggests that a significant fraction of CO is released continuously night and day by an active source situated at equatorial latitudes on the nucleus surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006263026604
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  • 2
    Electronic Resource
    Electronic Resource
    Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 5-11 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; C/1995 O1 (Hale-Bopp) ; radio observations ; molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract C/1995 O1 (Hale-Bopp) has been observed on a regular basis since August 1995 at millimetre and submillimetre wavelengths using IRAM, JCMT, CSO and SEST radio telescopes. The production rates of eight molecular species (CO, HCN, CH3OH, H2CO,H2S, CS, CH3CN,HNC) have been monitored as a function of heliocentric distance(rh from 7 AU pre-perihelion to 4 AU post-perihelion. As comet Hale-Bopp approached and receded from the Sun, these species displayed different behaviours. Far from the Sun, the most volatile species were found in general relatively more abundant in the coma. In comparison to other species, HNC, H2CO and CS showed a much steeper increase of the production rate with decreasing rh. Less than 1.5 AU from the Sun, the relative abundances were fairly stable and approached those found in other comets near 1 AU. The kinetic temperature of the coma, estimated from the relative intensities of the CH3OH and CO lines, increased with decreasing rh, from about10 K at 7 AU to 110 K around perihelion. The expansion velocity of the gaseous species, derived from the line shapes, also increased with a law close torh 3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006229818484
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  • 3
    Electronic Resource
    Electronic Resource
    Sub-mm and far-infrared continuum observations of herbig-haro exciting stars and other yso's (1995)
    Springer
    Astrophysics and space science 224 (1995), S. 85-88 
    Details
    ISSN: 1572-946X
    Keywords: Young Stellar Objects ; Dust
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show initial results from a survey of the mm to far-IR continuum spectra of ∼ 30 YSO's known to be exciting Herbig-Haro objects. The data are also compared with line intensities of C18O and H2CO. We include in this analysis results from other sub-mm continuum surveys of compact HII regions, T-Tauri stars and class 0 YSO's. The results provide a statistical sample of the long-wavelength dust spectra of ∼ 60 Young Stellar Objects. Data are displayed on mm to FIR colour-colour diagrams, with the aim of trying to discriminate between different stages of star formation through general spectral characteristics, rather than detailed model fits to individual sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667827
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  • 4
    Electronic Resource
    Electronic Resource
    A Molecular Survey of Comet C/1995 O1 (Hale-Bopp) at the IRAM Telescopes (1997)
    Springer
    Earth, moon and planets 78 (1997), S. 67-67 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Spectroscopic observations of comet Hale-Boppwere undertaken near perihelion at millimetre wavelengths with the Institut de Radioastronomie Millimétrique (IRAM) telescopes at Plateau de Bure (France)and Pico Veleta (Spain). They resulted in the first detections of HCOOH,SO2, NH2CHO and HCOOCH3 in a comet. HDO was detected through its312–221 line at 225.897 GHz,complementing the observation of the 101–000 line at 464.925 GHz at the James Clerk Maxwell Telescope (Meier et al., 1998,Science 279, 842).Several unidentified lines are present in the spectra. Observations of HC3N, HNCO, OCS, SO, CN, CO+, HCO+, in addition to more ‘classical’species CO, HCN, HNC, CH3CN, CH3OH, H2CO, CS and H2S (Biveret al., this issue) permit us to make out an extensive inventory of the composition of the coma of comet Hale-Bopp at its perihelion. It presents strong analogies with gas-phase abundances measured in interstellar hot cores and bipolar flows, which are believed to reflect the composition of interstellar grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006223428421
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  • 5
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    Gas and dust around A-type stars at tens of Myr: signatures of cometary breakup (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-25
    Description: Discs of dusty debris around main-sequence stars indicate fragmentation of orbiting planetesimals, and for a few A-type stars, a gas component is also seen that may come from collisionally released volatiles. Here we find the sixth example of a CO-hosting disc, around the ~30 Myr-old A0-star HD 32997. Two more of these CO-hosting stars, HD 21997 and 49 Cet, have also been imaged in dust with SCUBA-2 within the SCUBA-2 Survey of Nearby Stars project. A census of 27 A-type debris hosts within 125 pc now shows 7/16 detections of carbon-bearing gas within the 5–50 Myr epoch, with no detections in 11 older systems. Such a prolonged period of high fragmentation rates corresponds quite well to the epoch when most of the Earth was assembled from planetesimal collisions. Recent models propose that collisional products can be spatially asymmetric if they originate at one location in the disc, with CO particularly exhibiting this behaviour as it can photodissociate in less than an orbital period. Of the six CO-hosting systems, only β Pic is in clear support of this hypothesis. However, radiative transfer modelling with the ProDiMo code shows that the CO is also hard to explain in a proto-planetary disc context.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Early science with the Large Millimetre Telescope: Deep LMT/AzTEC millimetre observations of {epsilon} Eridani and its surroundings (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-24
    Description: Eridani is a nearby, young Sun-like star that hosts a ring of cool debris analogous to the Solar system's Edgeworth–Kuiper belt. Early observations at (sub-)mm wavelengths gave tentative evidence of the presence of inhomogeneities in the ring, which have been ascribed to the effect of a putative low eccentricity planet, orbiting close to the ring. The existence of these structures has been recently challenged by high-resolution interferometric millimetre observations. Here, we present the deepest single-dish image of Eridani at millimetre wavelengths, obtained with the Large Millimetre Telescope Alfonso Serrano (LMT). The main goal of these LMT observations is to confirm (or refute) the presence of non-axisymmetric structure in the disc. The dusty ring is detected for the first time along its full projected elliptical shape. The radial extent of the ring is not spatially resolved and shows no evidence, to within the uncertainties, of dust density enhancements. Additional features of the 1.1 mm map are: (i) the presence of significant flux in the gap between the ring and the star, probably providing the first exo-solar evidence of Poynting–Robertson drag, (ii) an unambiguous detection of emission at the stellar position with a flux significantly above that expected from Eridani's photosphere, and (iii) the identification of numerous unresolved sources which could correspond to background dusty star-forming galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Exocometary gas in the HD 181327 debris ring (2016)
    Oxford University Press
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    Publication Date: 2016-06-17
    Description: An increasing number of observations have shown that gaseous debris discs are not an exception. However, until now, we only knew of cases around A stars. Here we present the first detection of 12 CO (2–1) disc emission around an F star, HD 181327, obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with radiative transfer calculations, we study the dust and CO mass distribution. We find the dust is distributed in a ring with a radius of 86.0 ± 0.4 au and a radial width of 23.2 ± 1.0 au. At this frequency, the ring radius is smaller than in the optical, revealing grain size segregation expected due to radiation pressure. We also report on the detection of low-level continuum emission beyond the main ring out to ~200 au. We model the CO emission in the non-local thermodynamic equilibrium regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging between 1.2  x 10 –6  M and 2.9 x 10 –6 M , depending on the gas kinetic temperature and collisional partners densities. The CO densities and location suggest a secondary origin, i.e. released from icy planetesimals in the ring. We derive a CO+CO 2 cometary composition that is consistent with Solar system comets. Due to the low gas densities, it is unlikely that the gas is shaping the dust distribution.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    CO mass upper limits in the Fomalhaut ring - the importance of NLTE excitation in debris discs and future prospects with ALMA (2015)
    Oxford University Press
    Details
    Publication Date: 2015-02-01
    Description: In recent years, gas has been observed in an increasing number of debris discs, though its nature remains to be determined. Here, we analyse CO molecular excitation in optically thin debris discs, and search Atacama Large Millimeter/submillimeter Array (ALMA) Cycle-0 data for CO J  = 3–2 emission in the Fomalhaut ring. No significant line emission is observed; we set a 3 upper limit on the integrated line flux of 0.16 Jy km s –1 . We show a significant dependence of the CO excitation on the density of collisional partners n , on the gas kinetic temperature T k and on the ambient radiation field J , suggesting that assumptions widely used for protoplanetary discs (e.g. local thermodynamic equilibrium, LTE) do not necessarily apply to their low density debris counterparts. When applied to the Fomalhaut ring, we consider a primordial origin scenario where H 2 dominates collisional excitation of CO, and a secondary origin scenario dominated by e – and H 2 O. In either scenario, we obtain a strict upper limit on the CO mass of 4.9 10 –4 M . This arises in the non-LTE regime, where the excitation of the molecule is determined solely by the well-known radiation field. In the secondary scenario, assuming any CO present to be in steady state allows us to set an upper limit of ~55 per cent on the CO/H 2 O ice ratio in the parent planetesimals. This could drop to ~3 per cent if LTE applies, covering the range observed in Solar system comets (0.4–30 per cent). Finally, in light of our analysis, we present prospects for CO detection and characterization in debris discs with ALMA.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Resolving the planetesimal belt of HR 8799 with ALMA (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-19
    Description: The star HR 8799 hosts one of the largest known debris discs and at least four giant planets. Previous observations have found evidence for a warm belt within the orbits of the planets, a cold planetesimal belt beyond their orbits and a halo of small grains. With the infrared data, it is hard to distinguish the planetesimal belt emission from that of the grains in the halo. With this in mind, the system has been observed with ALMA in band 6 (1.34 mm) using a compact array format. These observations allow the inner edge of the planetesimal belt to be resolved for the first time. A radial distribution of dust grains is fitted to the data using an MCMC method. The disc is best fitted by a broad ring between $145^{+12}_{-12}$ au and $429^{+37}_{-32}$ au at an inclination of $40^{+5}_{-6}{^{\circ }}$ and a position angle of $51^{+8}_{-8}{^{\circ }}$ . A disc edge at ~145 au is too far out to be explained simply by interactions with planet b, requiring either a more complicated dynamical history or an extra planet beyond the orbit of planet b.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    ALMA observations of the {eta} Corvi debris disc: inward scattering of CO-rich exocomets by a chain of 3-30 M{oplus} planets? (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-16
    Description: While most of the known debris discs present cold dust at tens of astronomical unit (au), a few young systems exhibit hot dust analogous to the Zodiacal dust. Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here, we present ALMA observations of Corvi with a resolution of 1.2 arcsec (~22 au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152 au and radial full width at half-maximum of 46 au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4 detection of CO at ~20 au. CO could be released in situ from icy planetesimals being passed in when crossing the H 2 O or CO 2 ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75–100 au, with a mass of 3–30 M and an eccentricity 〈0.08. Such a planet would be able to clear its chaotic zone on a time-scale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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